1. Technical Field
This invention is related to the improvement of a hard alloy particle dispersion type wear resisting sintered ferro alloy.
2. Background Art
In the various fields, demand for ferro alloy with higher wear resistance becomes stronger. For example, according to the current trend of automotive internal combustion engine toward higher speed and higher performance, higher wear resistance has been required for the ferro alloy as a material for forming valve seats to be installed on an induction port and exhaust port of the engine. In order to answer such demand, Japanese Patent First Publication No. 53-81410 and Japanese patent Second (allowed) publication No. 57-3741 proposes a ferro alloy containing hard alloy dispersed in a base matrix.
As is well known, hard alloy has relatively low sintering ability. Therefore, when using hard alloy as particles for dispersion, it tends to cause formation of gaps in the sintered body and provides relatively weak coupling with the material of the base matrix. As a result, spalling of the hard alloy particle which is dispersed in the base matrix can occur to cause degradation of wear resistance of the ferro alloy, which can be lowered substantially. Therefore, if such a ferro alloy is used for forming the valve seat of the automotive engine, it may raise a problem of durability.
To protect hard alloy from wearing, it has been attempted to improve sintering by raising the sintering temperature, strengthening the alloy, and preventing the hard alloy from spalling by infiltrating Cu into gaps in the sintered alloy.
However, there remain some problems. Raising the sintering temperature causes the elements of the hard alloy to diffuse and in some cases, causes loss of or degradation of its property as a hard alloy. For this reason, it is necessary to restrict and control the range of the sintering temperature. This causes extra steps to be taken, thereby lowering productivity and raising the cost of production. Additionally, when using Cu for infiltration Cu and ferro alloy are layered while heating. These steps are time consuming and again cause for lower productivity and high production costs.
A sintered substance of high speed steel particles is used for valve seat material in Europe. Though as a material for valve seats it has substantial wear resistance, it has about five times the production cost of using particles of hard alloy material, and a sintered substance of high speed steel has not enough wear resistance against automotive engines having high revolution speeds, such as Japanese automotive vehicles.
In view of the drawbacks in the prior art, the present invention is intended to provide a method of forming a ferro alloy having higher wear resistance which is suitable to use in forming valve seats of automotive engines, for example.